The term “free will” has so many diverse connotations that I’m obliged to define it before I explain why we don’t have it. I construe free will the way I think most people do: At the moment when you have to decide among alternatives, you have free will if you could have chosen otherwise. To put it more technically, if you could rerun the tape of your life up to the moment you make a choice, with every aspect of the universe configured identically, free will means that your choice could have been different.

Although we can’t really rerun that tape, this sort of free will is ruled out, simply and decisively, by the laws of physics. Your brain and body, the vehicles that make “choices,” are composed of molecules, and the arrangement of those molecules is entirely determined by your genes and your environment. Your decisions result from molecular-based electrical impulses and chemical substances transmitted from one brain cell to another. These molecules must obey the laws of physics, so the outputs of our brain—our “choices”—are dictated by those laws. (It’s possible, though improbable, that the indeterminacy of quantum physics may tweak behavior a bit, but such random effects can’t be part of free will.) And deliberating about your choices in advance doesn’t help matters, for that deliberation also reflects brain activity that must obey physical laws.

To assert that we can freely choose among alternatives is to claim, then, that we can somehow step outside the physical structure of our brain and change its workings. That is impossible. Like the output of a programmed computer, only one choice is ever physically possible: the one you made. As such, the burden of proof rests on those who argue that we can make alternative choices, for that’s a claim that our brains, unique among all forms of matter, are exempt from the laws of physics by a spooky, nonphysical “will” that can redirect our own molecules.

My claim that free will as defined above is an illusion leads to a prediction: Our sense of controlling our actions might sometimes be decoupled from those actions themselves. Recent experiments in cognitive science show that some deliberate acts occur before they reach our consciousness (typing or driving, for example), while in other cases, brain scans can predict our choices several seconds before we’re conscious of having made them. Additionally, stimulation of the brain, or clever psychological experiments, can significantly increase or decrease our sense of control over our choices.

So what are the consequences of realizing that physical determinism negates our ability to choose freely? Well, nihilism is not an option: We humans are so constituted, through evolution or otherwise, to believe that we can choose. What is seriously affected is our idea of moral responsibility, which should be discarded along with the idea of free will. If whether we act well or badly is predetermined rather than a real choice, then there is no moral responsibility—only actions that hurt or help others. That realization shouldn’t seriously change the way we punish or reward people, because we still need to protect society from criminals, and observing punishment or reward can alter the brains of others, acting as a deterrent or stimulus. What we should discard is the idea of punishment as retribution, which rests on the false notion that people can choose to do wrong.

The absence of real choice also has implications for religion. Many sects of Christianity, for example, grant salvation only to those who freely choose Jesus as their savior. And some theologians explain human evil as an unavoidable by product of God’s gift of free will. If free will goes, so do those beliefs. But of course religion won’t relinquish those ideas, for such important dogma is immune to scientific advances.

Finally, on the lighter side, knowing that we don’t have free will can perhaps temper our sense of regret or self-recrimination, since we never had real choices in our past. No, we couldn’t have had that V8, and Robert Frost couldn’t have taken the other road.

Although science strongly suggests that free will of the sort I defined doesn’t exist, this view is unpopular because it contradicts our powerful feeling that we make real choices. In response, some philosophers—most of them determinists who agree with me that our decisions are preordained—have redefined free will in ways that allow us to have it. I see most of these definitions as face-saving devices designed to prop up our feeling of autonomy. To eliminate the confusion produced by multiple and contradictory concepts of free will, I propose that we reject the term entirely and adopt the suggestion of the cognitive scientist Marvin Minsky: Instead of saying my decision arises from free will, we might say, “My decision was determined by internal forces I do not understand.”

Jerry A. Coyne is a professor in the department of ecology and evolution at the University of Chicago.